CVE-2026-5751 - justhtml before 1.14.0 Mutation XSS via custom sanitization policies
Brief
CVE ID : CVE-2026-5751
Published : Aug. 23, 2026, 2:16 p. m.
- 2 hours, 54 minutes ago
Description : justhtml versions 1.
- 0 and earlier contain a parser-differential / mutation cross-site scripting (mXSS) vulnerability when using a custom SanitizationPolicy that preserves foreign namespaces (e. g. , drop_foreign_namespaces=False with allowlisted SVG/MathML elements or raw-text containers such as ).
Specially crafted input can sanitize into markup that appears safe but becomes unsafe when re-parsed by a browser or another HTML parser, allowing markup injection. The default safe configuration (sanitize=True) is not affected. Fixed in 1.
- 0.
Severity: 6.1
- MEDIUM
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